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5 Commits

Author SHA1 Message Date
Moe Charm (CI)
6b38bc840e Cleanup: Remove unused hakmem_libc.c (duplicate of hakmem_syscall.c) 
- File was not included in Makefile OBJS_BASE
- Functions already implemented in hakmem_syscall.c
- Size: 361 bytes removed
 2025-11-26 13:03:17 +09:00
Moe Charm (CI)
d8168a2021 Fix C7 TLS SLL header restoration regression + Document Larson MT race condition 
## Bug Fix: Restore C7 Exception in TLS SLL Push

**File**: `core/box/tls_sll_box.h:309`

**Problem**: Commit 25d963a4a (Code Cleanup) accidentally reverted the C7 fix by changing:
```c
if (class_idx != 0 && class_idx != 7) {  // CORRECT (commit 8b67718bf)
if (class_idx != 0) {                     // BROKEN (commit 25d963a4a)
```

**Impact**: C7 (1024B class) header restoration in TLS SLL push overwrote next pointer at base[0], causing corruption.

**Fix**: Restored `&& class_idx != 7` check to prevent header restoration for C7.

**Why C7 Needs Exception**:
- C7 uses offset=0 (stores next pointer at base[0])
- User pointer is at base+1
- Next pointer MUST NOT be overwritten by header restoration
- C1-C6 use offset=1 (next at base[1]), so base[0] header restoration is safe

## Investigation: Larson MT Race Condition (SEPARATE ISSUE)

**Finding**: Larson still crashes with 3+ threads due to UNRELATED multi-threading race condition in unified cache freelist management.

**Root Cause**: Non-atomic freelist operations in `TinySlabMeta`:
```c
typedef struct TinySlabMeta {
    void* freelist;    // ❌ NOT ATOMIC
    uint16_t used;     // ❌ NOT ATOMIC
} TinySlabMeta;
```

**Evidence**:
```
1 thread:  ✅ PASS (1.88M - 41.8M ops/s)
2 threads: ✅ PASS (24.6M ops/s)
3 threads: ❌ SEGV (race condition)
4+ threads: ❌ SEGV (race condition)
```

**Status**: C7 fix is CORRECT. Larson crash is separate MT issue requiring atomic freelist implementation.

## Documentation Added

Created comprehensive investigation reports:
- `LARSON_CRASH_ROOT_CAUSE_REPORT.md` - Full technical analysis
- `LARSON_DIAGNOSTIC_PATCH.md` - Implementation guide
- `LARSON_INVESTIGATION_SUMMARY.md` - Executive summary
- `LARSON_QUICK_REF.md` - Quick reference
- `verify_race_condition.sh` - Automated verification script

## Next Steps

Implement atomic freelist operations for full MT safety (7-9 hour effort):
1. Make `TinySlabMeta.freelist` atomic with CAS loop
2. Audit 87 freelist access sites
3. Test with Larson 8+ threads

🔧 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
 2025-11-22 02:15:34 +09:00
Moe Charm (CI)
25d963a4aa Code Cleanup: Remove false positives, redundant validations, and reduce verbose logging 
Following the C7 stride upgrade fix (commit 23c0d9541), this commit performs
comprehensive cleanup to improve code quality and reduce debug noise.

## Changes

### 1. Disable False Positive Checks (tiny_nextptr.h)
- **Disabled**: NXT_MISALIGN validation block with `#if 0`
- **Reason**: Produces false positives due to slab base offsets (2048, 65536)
  not being stride-aligned, causing all blocks to appear "misaligned"
- **TODO**: Reimplement to check stride DISTANCE between consecutive blocks
  instead of absolute alignment to stride boundaries

### 2. Remove Redundant Geometry Validations

**hakmem_tiny_refill_p0.inc.h (P0 batch refill)**
- Removed 25-line CARVE_GEOMETRY_FIX validation block
- Replaced with NOTE explaining redundancy
- **Reason**: Stride table is now correct in tiny_block_stride_for_class(),
  defense-in-depth validation adds overhead without benefit

**ss_legacy_backend_box.c (legacy backend)**
- Removed 18-line LEGACY_FIX_GEOMETRY validation block
- Replaced with NOTE explaining redundancy
- **Reason**: Shared_pool validates geometry at acquisition time

### 3. Reduce Verbose Logging

**hakmem_shared_pool.c (sp_fix_geometry_if_needed)**
- Made SP_FIX_GEOMETRY logging conditional on `!HAKMEM_BUILD_RELEASE`
- **Reason**: Geometry fixes are expected during stride upgrades,
  no need to log in release builds

### 4. Verification
- Build: ✅ Successful (LTO warnings expected)
- Test: ✅ 10K iterations (1.87M ops/s, no crashes)
- NXT_MISALIGN false positives: ✅ Eliminated

## Files Modified
- core/tiny_nextptr.h - Disabled false positive NXT_MISALIGN check
- core/hakmem_tiny_refill_p0.inc.h - Removed redundant CARVE validation
- core/box/ss_legacy_backend_box.c - Removed redundant LEGACY validation
- core/hakmem_shared_pool.c - Made SP_FIX_GEOMETRY logging debug-only

## Impact
- **Code clarity**: Removed 43 lines of redundant validation code
- **Debug noise**: Reduced false positive diagnostics
- **Performance**: Eliminated overhead from redundant geometry checks
- **Maintainability**: Single source of truth for geometry validation

🧹 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
 2025-11-21 23:00:24 +09:00
Moe Charm (CI)
29fefa2018 P0 Lock Contention Analysis: Instrumentation + comprehensive report 
**P0-2: Lock Instrumentation** (✅ Complete)
- Add atomic counters to g_shared_pool.alloc_lock
- Track acquire_slab() vs release_slab() separately
- Environment: HAKMEM_SHARED_POOL_LOCK_STATS=1
- Report stats at shutdown via destructor

**P0-3: Analysis Results** (✅ Complete)
- 100% contention from acquire_slab() (allocation path)
- 0% from release_slab() (effectively lock-free!)
- Lock rate: 0.206% (TLS hit rate: 99.8%)
- Scaling: 4T→8T = 1.44x (sublinear, lock bottleneck)

**Key Findings**:
- 4T: 330 lock acquisitions / 160K ops
- 8T: 658 lock acquisitions / 320K ops
- futex: 68% of syscall time (from previous strace)
- Bottleneck: acquire_slab 3-stage logic under mutex

**Report**: MID_LARGE_LOCK_CONTENTION_ANALYSIS.md (2.3KB)
- Detailed breakdown by code path
- Root cause analysis (TLS miss → shared pool lock)
- Lock-free implementation roadmap (P0-4/P0-5)
- Expected impact: +50-73% throughput

**Files Modified**:
- core/hakmem_shared_pool.c: +60 lines instrumentation
  - Atomic counters: g_lock_acquire/release_slab_count
  - lock_stats_init() + lock_stats_report()
  - Per-path tracking in acquire/release functions

**Next Steps**:
- P0-4: Lock-free per-class free lists (Stage 1: LIFO stack CAS)
- P0-5: Lock-free slot claiming (Stage 2: atomic bitmap)
- P0-6: A/B comparison (target: +50-73%)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
 2025-11-14 15:32:07 +09:00
Moe Charm (CI)
1010a961fb Tiny: fix header/stride mismatch and harden refill paths 
- Root cause: header-based class indexing (HEADER_CLASSIDX=1) wrote a 1-byte
  header during allocation, but linear carve/refill and initial slab capacity
  still used bare class block sizes. This mismatch could overrun slab usable
  space and corrupt freelists, causing reproducible SEGV at ~100k iters.

Changes
- Superslab: compute capacity with effective stride (block_size + header for
  classes 0..6; class7 remains headerless) in superslab_init_slab(). Add a
  debug-only bound check in superslab_alloc_from_slab() to fail fast if carve
  would exceed usable bytes.
- Refill (non-P0 and P0): use header-aware stride for all linear carving and
  TLS window bump operations. Ensure alignment/validation in tiny_refill_opt.h
  also uses stride, not raw class size.
- Drain: keep existing defense-in-depth for remote sentinel and sanitize nodes
  before splicing into freelist (already present).

Notes
- This unifies the memory layout across alloc/linear-carve/refill with a single
  stride definition and keeps class7 (1024B) headerless as designed.
- Debug builds add fail-fast checks; release builds remain lean.

Next
- Re-run Tiny benches (256/1024B) in debug to confirm stability, then in
  release. If any remaining crash persists, bisect with HAKMEM_TINY_P0_BATCH_REFILL=0
  to isolate P0 batch carve, and continue reducing branch-miss as planned.
 2025-11-09 18:55:50 +09:00